Field of the Invention
The present invention relates to an intermediate transfer belt (seamless belt) which is mounted in image forming apparatuses such as copiers, printers or the like, and is suitable for full-color image formation, a method for producing the intermediate transfer belt, and an electrophotographic apparatus using the intermediate transfer belt.
Description of the Related Art
Conventionally, in electrophotographic image forming apparatuses, seamless belts have been used as members for various applications. Particularly, in full-color electrophotographic apparatuses of recent years, an intermediate transfer belt system is used, in which development images of four colors: yellow, magenta, cyan, black, are superimposed on an intermediate transfer medium, and then the superimposed images are collectively transferred to a transfer medium, such as paper.
In such intermediate transfer belt system, with respect to a photoconductor four developing units are used, but use of such intermediate transfer belt system has a disadvantage that print speed is slow. For high speed printing, a four-series tandem system is used in which photoconductors for four colors are arranged in a tandem manner, and each color is continuously transferred on paper. However, in this system, it is difficult to achieve accurate registration upon superimposing respective images because of change of paper condition due to environment, causing out-of-color registration. Thus, recently, an intermediate transfer system has been predominately applied in the four-series tandem system.
For this reason, characteristics required for the intermediate transfer belt have been tough to achieve, such as high speed transfer, positional accuracy, etc., but it is necessary to satisfy those characteristics. Particularly, it is demanded to inhibit variation in positional accuracy caused by deformation such as elongation of a belt itself due to continuous use. The intermediate transfer belt is required to be heat resistant and flame retardant, because it occupies a large area of an apparatus and a high voltage is applied thereto for transferring an image. In order to satisfy these demands, as an intermediate transfer belt material, a polyimide resin, and a polyamideimide resin, which have high elasticity and high heat resistance, are used.
However, an intermediate transfer belt made of a polyimide resin has high strength and thus high surface hardness. Therefore, in transferring a toner image, a high pressure is applied to the toner layer. As a result, the toner is locally aggregated, resulting in that part of the image is not transferred in some cases to form a so-called spot-containing image. Also, such an intermediate transfer belt has poor followability to a photoconductor, paper, etc., which are brought into contact with the intermediate transfer belt at transfer positions. Such poor followability may cause insufficient contact portions (spaces) at the transfer positions, leading to uneven transfer.
In recent years, full-color electrophotographic image formation is often performed on various types of paper, such as commonly-used smooth paper, highly-smooth papers with slip properties (e.g., coated papers) and rough paper (e.g., recycled paper, embossed paper, Japanese paper and kraft paper). In the full-color electrophotographic image formation, followability to such papers that have various surface conditions is important. Poor followability causes unevenness in image density and color toner following irregularities of paper.
In order to solve this problem, various intermediate transfer belts have been proposed which contain a base layer and a relatively flexible layer laminated on the base layer.
However, when the relatively flexible layer is used as a surface layer, the pressure during transfer may be reduced. In addition, although the followability to irregularities of paper is improved, toner cannot be separated from the surface layer since the toner releasability of the surface is poor. As a result, the transfer efficiency is decreased while the followability is improved. Furthermore, such a surface layer is problematically degraded in wear resistance and abrasion resistance.
In order to solve this problem, methods have been proposed in which a protective layer is further provided. The protective layer made of a material having sufficiently high transferability cannot comply with the flexible layer and is unfavorably cracked or peeled off. In other proposals, provision of fine particles in the surface improves transferability.
Specifically, Japanese Patent Application Laid-Open (JP-A) No. 09-230717 proposes that beads having a diameter of 3 μm or smaller are coated.
However, in the technique disclosed in this patent literature, the particles tend to be exfoliated. Thus, this technique is not sufficient to meet the requirements for the recent electrophotographic apparatuses.
Also, JP-A Nos. 2002-162767 and 2004-354716 proposed that a layer is formed from a material having an affinity to hydrophobidized fine particles. In these patent literatures, particles having a very small particle diameter are preferably used.
However, the particle layer is thick and has ununiform areas formed due to aggregation of the particles, causing variation in transferability. This technique is not sufficient to meet the requirements for the formation of high-quality images by the recent electrophotographic apparatuses.
Moreover, JP-A Nos. 2007-328165 and 2009-75154 proposed that relatively large particles are partially embedded in the surface resin layer to realize satisfactory durability. However, even in these proposals, the particles are stacked in the thickness direction, and some of the particles are completely embedded in the resin layer, resulting in that the particles are ununiformly present in the layer. This technique is also not sufficient to meet the requirements for the formation of high-quality images by the recent electrophotographic apparatuses.
In any of the techniques disclosed in JP-A Nos. 09-230717, 2002-162767, 2004-354716, 2007-328165 and 2009-75154, silica particles are preferably used. The silica particles strongly aggregate together and thus, as described above, a uniform particle layer cannot be formed. Furthermore, such inorganic particles as silica tend to scratch and abrade the surface of an organic photoconductor, which is suitably used as an image bearing member responsible for image formation, when comes into contact with the organic photoconductor at the transfer position, causing a failure of degrading durability.